Composite dielectric layers

ABSTRACT

An apparatus including a contact point on a substrate; a first dielectric layer comprising a material having a dielectric constant less than five formed on the contact point, and a different second dielectric layer formed on the substrate and separated from the contact point by the first dielectric layer. Collectively, the first and second dielectric layers comprise a composite dielectric layer having a composite dielectric constant value. The contribution of the first dielectric layer to the composite dielectric value is up to 20 percent. Also, a method including depositing a composite dielectric layer over a contact point on a substrate, the composite dielectric layer comprising a first material having a dielectric constant less than 5 and a second different second material, and forming a conductive interconnection through the composite dielectric layer to the contact point.

BACKGROUND

1. Field

Integrated circuit processing and, more particularly, to the patterningof interconnections on an integrated circuit.

2. Background

Modern integrated circuits use conductive interconnections to connectthe individual devices on a chip or to send or receive signals externalto the chip. Popular types of interconnection include aluminum alloyinterconnections and copper interconnections.

One process used to form interconnections, particularly copperinterconnections, is a damascene process. In a damascene process, atrench is cut in a dielectric and filled with copper to form theinterconnection. A via may be in the dielectric beneath the trench witha conductive material in the via to couple the interconnection tounderlying integrated circuit devices or underlying interconnections. Inone damascene process (a “dual damascene process”), the trench and viaare each filled with copper material by, for example, a singledeposition.

A photoresist is typically used over the dielectric to pattern a via ora trench or both in the dielectric for the interconnection. Afterpatterning, the photoresist is removed. The photoresist is typicallyremoved by an oxygen plasma (oxygen ashing). The oxygen used in theoxygen ashing can react with an underlying copper interconnection andoxidize the interconnection. Accordingly, damascene processes typicallyemploy a barrier layer of silicon nitride Si₃N₄ directly over the copperinterconnection to protect the copper from oxidation during oxygenashing in the formation of a subsequent level interconnection. Inintelayer interconnection levels (e.g., beyond a first level over adevice substrate), the barrier layer also protects against misguided orunlanded vias extending to an underlying dielectric layer or level.

In general, the Si₃N₄ barrier layer is very thin, for example, roughly10 percent of the thickness of the pre-metal dielectric (PMD) layer orinterlayer dielectric (ILD) layer. A thin barrier layer is preferredprimarily because Si₃N₄ has a relatively high dielectric constant (k) onthe order of 6-7. The dielectric constant of a dielectric material, suchas an interlayer dielectric, generally describes the parasiticcapacitance of the material. As the parasitic capacitance is reduced,the cross-talk (e.g., a characterization of the electric field betweenadjacent interconnections) is reduced, as is the resistance-capacitance(RC) time delay and power consumption. Thus, the effective dielectricconstant (k_(eff)) of a PMD layer or ILD layer is defined by the thinbarrier layer and another dielectric material having a lower dielectricconstant so that the effect of the high dielectric material typicallyused for the barrier layer (e.g., Si₃N₄) is minimized. Representativedielectric materials for use in combination with a barrier layer to formPMD or ILD layers include silicon dioxide (SiO₂), fluorinated silicateglass (FSG), and carbon-doped oxide (CDO).

As technologies advance, the distance (e.g., pitch) betweeninterconnections decreases as more devices and more interconnections(e.g., interconnect lines) are formed on a structure. Thus, theeffective dielectric constant (k_(eff)) of a PMD or ILD layer issignificant.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view of a portion of a circuit substrate orinterconnect layer on a substrate including a contact point and abarrier layer formed over the contact point.

FIG. 2 shows the structure of FIG. 1 following the formation of adielectric layer on the barrier layer.

FIG. 3 shows the structure of FIG. 2 following the formation of aninterconnection to the contact point.

FIG. 4 is a schematic side view of a portion of a circuit substrateshowing a contact point and a barrier layer overlying the contact point.

FIG. 5 shows the structure of FIG. 4 following the introduction of asacrificial layer and the formation of an interconnection to the contactpoint.

FIG. 6 shows the structure of FIG. 5 following the removal of thesacrificial layer.

FIG. 7 shows the structure of FIG. 6 following the introduction of abarrier layer around the interconnection.

FIG. 8 shows the structure of FIG. 7 following the introduction of adielectric layer on the substrate.

FIG. 9 shows the structure of FIG. 8 following the introduction of abarrier layer on the substrate.

DETAILED DESCRIPTION

FIGS. 1-3 illustrate a dual damascene process for forming aninterconnection over a contact point. A contact point is, for example, adevice on a substrate (e.g., gate, junction, etc.). Alternatively, in amulti-level interconnection device configuration, the contact point alsoincludes an underlying interconnection (e.g., an interconnection line).A typical integrated circuit of a microprocessor may have, for example,five or more interconnection layers or lines stacked on one another,each insulated from one another by dielectric material.

FIG. 1 illustrates a cross-sectional, schematic side view of a portionof a circuit substrate structure. Structure 100 includes substrate 110of, for example, a semiconductor material such as silicon or asemiconductor layer on an insulator such as glass. Substrate 110includes contact point 120 on a surface thereof. In one embodiment,contact point 120 is a portion of an underlying interconnect line (e.g.,a metal trench). A representative interconnect line is shown in dashedlines. Overlying contact point 120 and substrate 110, in one embodiment,is barrier layer 130. Barrier layer 130 is selected, in one embodiment,to be a material having a dielectric constant (k) less than on the orderof about five. In the context of a contact point that is a copperinterconnection (e.g., interconnection line), barrier layer 130 isselected to have relatively good copper diffusion characteristics (i.e.,to inhibit copper diffusion). Barrier layer 130 is also selected suchthat it is a material that has an etch characteristic such that it maybe selectively etched or retained during an etch operation involvingbarrier layer 130 or a subsequently introduced dielectric material, suchas a dielectric material that, together with barrier material 130, willserve as a pre-metal dielectric (PMD) or interlayer dielectric (ILD)layer dielectric material. One material for barrier layer 130 is cubicboron nitride (CBN). Cubic boron nitride has a dielectric constant onthe order of 4-4.5. Cubic boron nitride may be introduced by chemicalvapor deposition (CVD) and tends to serve as an inhibitor of copperdiffusion when used as the barrier material in the context of copper.Further, cubic boron nitride is selectively etchable in, for example, afluorine plasma. Still further, cubic boron nitride is a relatively highcompressive stress material allowing, in one example, its use inconjunction with high tensile stress materials to minimize the effect ofthe tensile stress.

In one embodiment, barrier layer 130 of cubic boron nitride isintroduced, according to current technologies, to a thickness on theorder of 40 nanometers (nm) to 100 nm. The thickness is selected, in oneexample, to be sufficient to protect an underlying contact point 120(e.g., copper interconnection line), but not to unacceptably increasethe capacitance between contact point 120 and, for example; an overlyingor adjacent interconnection (e.g., thickness selected to minimize thecontribution of barrier layer 130 to k_(eff)).

Overlying barrier layer 130 in the illustration shown in FIG. 2 isdielectric layer 140. Dielectric layer 140 is, for example, a tetraethylorthosilicate (TEOS), a plasma enhanced CVD (PECVD), SiO₂, a fluorinatedsilicate glass (FSG), or a carbon-doped oxide (CDO) deposited to athickness on the order of approximately 700 nanometers according tocurrent technologies. As described in more detail with reference toFIGS. 4-9 and the accompanying text, dielectric layer 140 may also be anaerogel. The thickness of dielectric layer 140 will depend, in part, onsize characteristics and scaling considerations for the device.Collectively, barrier layer 130 and dielectric layer 140 define acomposite dielectric layer (e.g., PMD or ILD layer) having a compositeor an effective dielectric constant (k_(eff)). In one embodiment, thecontribution of the material selected for barrier layer 130 is less than20 percent, in another embodiment, less than 10 percent of the k_(eff).Once dielectric layer 140 is deposited and formed, the material may beplanarized, for example, with a polish (e.g., chemical-mechanicalpolish).

Referring to FIG. 3, following the introduction of dielectric layer 140,an opening is made to contact point 120. In one embodiment, the openingincludes via 160 and trench 170 formed, for example, by sequentialphotolithographic patterning and etching operations. Representatively,what is shown is a dual damescene process where via 160 and trench 170are formed as the opening and are filled with conductive material 150such as a copper material and the conductive material in trench 170serves as an interconnection line. Thus, although not shown in the crosssectional view of FIG. 3, trench 170 may extend into the page as viewedto act as a trench for a conductive material interconnection line toreside therein. In addition to conductive material of, for example, acopper material in via 160 and trench 170, one or more layers may bedeposited along the sidewalls of via 160 and trench 170 to, for example,inhibit diffusion of the conductive material and/or improve adhesion ofthe conductive material.

Via 160 opening is made through dielectric layer 140 and barriermaterial 130. To form an opening through dielectric layer 140, asuitable etchant is selected that does not substantially react ordisrupt underlying barrier material 130. In the case of a dielectriclayer 140 of FSG and barrier layer 130 of cubic boron nitride, asuitable etchant to etch FSG is, for example, a SiCl₄ etch chemistry.With such an etchant, an etch of dielectric layer 140 will proceedthrough the material and substantially stop when barrier material 130 isexposed. A subsequent etch chemistry, such as a fluorine-based etchchemistry (e.g., HF, CF₄) can then be used to form an opening throughbarrier material 130 and expose contact point 120.

After exposing contact point 120, conductive material 150 is depositedin trench 170 and via 160. A suitable conductive material is, forexample, a copper material deposited by a damascene process. Onceconductive material 150 is deposited in trench 170 and via 160, thesubstrate may be planarized. The process described above may then berepeated for a subsequent interconnection layer or layers.

FIGS. 4-9 describe a second embodiment. Referring to FIG. 4, structure200 in this embodiment includes substrate 210 having a contact point 220on a surface thereof. Contact point may be, for example, a device or aninterconnection formed over a substrate to one or more devices formed onor near the substrate.

Overlying contact point 220 (as viewed) on a surface of substrate 210 inthe structure of FIG. 4 is barrier layer 230. Barrier layer 230 may bedeposited, representatively, as a blanket over a portion, including theentire portion of the surface of substrate 210. Barrier layer 230 isselected to be a material having a dielectric constant (k) less than 5.In another embodiment, barrier layer 230 is a material selected to havegood copper diffusion characteristics and etch selectivity. Cubic boronnitride is one material that has such characteristics. Barrier layer 230of cubic boron nitride, in one example, has a thickness on the order 40nm to 100 nm.

FIG. 5 shows the structure of FIG. 4, following the introduction ofsacrificial layer 240 and the formation of trench 270, via 260 andconductive material 250 within the trench and via. Sacrificial layer 240may be, for example, a dielectric material such as SiO₂ or othermaterial that may be patterned to the exclusion of barrier material 230.Sacrificial layer 240 is deposited to a thickness sufficient (perhapsafter planarization) to accommodate a properly sized interconnectionline (in trench 270) and contact (in via 260). One suitable thicknessfor sacrificial layer 240 according to current techniques is on theorder of about 700 nanometers. As shown in FIG. 5, conductive material250 of, for example, copper material is formed in trench 270 and via 260and contacts contact point 220.

FIG. 6 shows the structure of FIG. 5 following the removal ofsacrificial material 240. In the embodiment, where sacrificial material240 is an oxide (e.g., SiO₂) and barrier material 230 is cubic boronnitride, sacrificial material 240 may be removed, by dipping structure200 in hydrofluoric acid. Alternatively, an etchant introduced without aphotolithographic mask overlying a portion of sacrificial material 240to protect the material from an etch chemistry may be used. As shown inFIG. 6, following the removal of sacrificial material 240, conductivematerial 250, such as a copper material, remains exposed on substrate210 of structure 200. In an embodiment where conductive material 250 iscopper, the exposure of conductive material 250 by removal ofsacrificial material 240 may be done in an inert or oxygen-freeenvironment to prevent oxidation of the copper material.

FIG. 7 shows the structure of FIG. 6 following the introduction ofbarrier layer 280. In one embodiment, barrier layer 280 is selected of amaterial having a dielectric constant less than 5. One suitable materialis cubic boron nitride. In this case, both barrier layer 230 and barrierlayer 280 are cubic boron nitride. As shown in FIG. 7, barrier layer 280completely surrounds conductive material 250.

In one embodiment, there may be many conductive structures such asconductive material 250 formed to various contact points on substrate210. A representative pitch between such structures (reference number255 in FIG. 6) may be on the order of about 70 nanometers according tocurrent technologies for interconnection lines. Accordingly, thethickness of barrier layer 280 is selected, in one embodiment, to besufficient to surround conductive material 250 but thin enough to leavean area between conductive material structures exposed so as, forexample, not to create voids between the structures. Where a pitchbetween conductive structures is on the order of about 70 nanometers, athickness of barrier layer 280 may representatively be on the order of30 to 40 nanometers.

FIG. 8 shows the structure of FIG. 7 following the introduction ofdielectric layer 290. In one embodiment, dielectric layer 290 isintroduced as a blanket layer over a portion, including the entireportion of the structure. Dielectric layer 290, in one embodiment, isselected to have a low dielectric constant, preferably a dielectricconstant less than two (2). In one embodiment, dielectric layer 290 isan aerogel (XLK). Aerogel is described as a porous glass and can have adielectric constant on the order of 1.1. Although aerogel has a lowdielectric constant, it is known to have inferior mechanical properties,being weak and brittle.

In one embodiment, dielectric layer 290 of aerogel may be introduced asa liquid, possibly through the use of a solvent. The material may thenbe dried (supercritical drying) to evaporate the solvent and form asolid dielectric material layer. Planarization may also be necessary toexpose barrier layer 280 over conductive material 250 or to exposeconductive material 250. In one embodiment, dielectric layer 290 of, forexample, aerogel, and barrier layer 280 act as the substrate surface foradditional layers. Collectively, barrier layer 230, barrier layer 280,and dielectric layer 290 define a composite dielectric layer (e.g., PMDor ILD layer) having a composite or an effective dielectric constant(k_(eff)). In one embodiment, the contribution of the material selectedfor barrier layer 280 and the material Selected for barrier layer 280 isless than 20 percent, in another embodiment less than 10 percent, of thek_(eff).

FIG. 9 shows the structure of FIG. 8 following the introduction ofbarrier layer 295 as, for example, a blanket over a portion, includingthe entire portion, the substrate surface. In one embodiment, barrierlayer 295 is similar to barrier layer 230 in that it has a dielectricconstant less than about 5 and acts as a suitable diffusion barrier fora conductive structure for which it may be in contact. It also may haverelatively good etch selectivity relative to a dielectric material that,together with barrier layer 295, forms an ILD. In one embodiment,barrier layer 295 is cubic boron nitride as is barrier layer 280 andbarrier layer 230. In this manner, dielectric 290 of, for example,aerogel is encapsulated by cubic boron nitride.

In the preceding detailed description, specific embodiments aredescribed. It will, however, be evident that various modifications andchanges may be made thereto without departing from the broader spiritand scope of the claims. The specification and drawings are,accordingly, to be regarded in an illustrative rather than a restrictivesense.

What is claimed is:
 1. An apparatus comprising: a contact point formedon a substrate or interconnect layer; a first dielectric layercomprising cubic boron nitride on the contact point; and a differentsecond dielectric layer formed on the substrate and separated from thecontact point by the first dielectric layer.
 2. The apparatus of claim1, wherein collectively the first dielectric layer and the seconddielectric layer comprise a composite dielectric layer having acomposite dielectric constant value and the contribution of the firstdielectric layer to the composite dielectric constant value is up to 20percent, and the composite dielectric value is less than 3.0.
 3. Theapparatus of claim 1, wherein, collectively, the first dielectric layerand the second dielectric layer comprise a composite dielectric layer,the apparatus further comprising: an interconnection line formed on thesecond dielectric layer and coupled to the first interconnection line bya contact through the composite dielectric layer.
 4. The apparatus ofclaim 3, wherein the contact has a body with a length dimensionextending through the composite dielectric layer and a third dielectricmaterial comprising a dielectric constant similar to the material of thefirst dielectric layer is formed on the length dimension of the bodybetween the contact and the second dielectric layer.
 5. The apparatus ofclaim 4, wherein the material of the third dielectric layer comprisescubic boron nitride.
 6. The apparatus of claim 5, further comprising afourth dielectric layer formed on the substrate and separated from thefirst dielectric layer by the second dielectric layer.
 7. The apparatusof claim 6, wherein the fourth dielectric layer comprises a materialsimilar to the material of the first dielectric layer.
 8. The apparatusof claim 7, wherein the material of the fourth dielectric layercomprises cubic boron nitride.
 9. The apparatus of claim 1, wherein thesecond dielectric layer comprises an aerogel.
 10. An apparatuscomprising: a contact point formed on a substrate; a dielectric layerformed on substrate; and an interconnection formed through thedielectric layer to the contact point wherein the dielectric layercomprises a first dielectric material comprising cubic boron nitride anda second different dielectric material, the first dielectric materialencapsulating the second dielectric material.
 11. The apparatus of claim10, wherein the first dielectric material comprises a dielectricconstant less than
 5. 12. The apparatus of claim 10, wherein theinterconnection is in one of multiple levels of interconnections on thesubstrate other than an initial level adjacent the substrate.
 13. Theapparatus of claim 10, wherein the second dielectric material comprisesan aerogel.
 14. A method comprising: depositing a composite dielectriclayer over a contact point on a substrate, the composite dielectriclayer comprising a first material comprising cubic boron nitride and asecond different material; and forming a conductive interconnectionthrough the composite dielectric layer to the contact point.
 15. Themethod of claim 14, wherein depositing a composite dielectric layercomprises depositing a material comprising a dielectric constant similarto the first material on the interconnection.
 16. The method of claim14, wherein depositing a composite dielectric layer comprisesencapsulating the second material with the first material.